The invention relates to a gear shift device for vehicles with a mechanical, manually operable gearbox which is provided between an engine and driving wheels for the vehicle, wherein the gearbox can be operated by means of a gear lever, which is linked to a signal transmitter, which is connected via a transmission device to a signal receiver for movement of components of the gearbox for engagement or disengagement of gears, and the gear lever is arranged to be brought from a position wherein a gear is engaged, to a position wherein another gear is engaged, via a neutral position, i.e. a position wherein no gear is engaged.
Gear shift devices of the above-mentioned type are known from the prior art. For example, from NO 171426 a gear shift device is known, wherein the signal transmitter is composed of two hydraulic master cylinders, which can be operated by means of the gear lever. The connecting device comprises hydraulic lines, and the signal receiver comprises two hydraulic slave cylinders. The gear lever has a knob which can be moved along an H-shaped path with two parallel legs which are connected to a path portion extending across the legs. When the knob is moved along the transverse portion and one of the slave cylinders is operated by means of one of the master cylinders, it is moved from one leg to the other. The gears can be engaged by moving the knob from the transverse path portion to the ends of the respective legs. The second slave cylinder is hereby operated by the second master cylinder. When the knob is located on the transverse path portion, the engine is thereby not operationally connected to the driving wheels and this position of the knob can also be called a neutral position.
Furthermore, from U.S. Pat. No. 5,595,551 a mechanical, multistage, automatic gearbox is known, where the gear shift devices comprise an electronic control device which is arranged to receive signals from a number of sensors which measure driving parameters such as engine rotational frequency and power, vehicle speed, etc., and depending on the measurements determines which gear ratio is best and selects a corresponding gear. With such automatic gearboxes, moreover, a semi-automatic mode of operation may often be chosen, where, by operating an electrical switch, the vehicle's driver can select a gear, which is then engaged automatically, i.e. without special operation of a clutch pedal or accelerator, the gearbox and possibly the clutch being operated by an electronically controlled, mechanical device which performs the change of gear in the gearbox and the clutch. In the event of a failure in the electrical system or a failure of the mechanical device, a gearbox of this type cannot be operated, either in the automatic or the semi-automatic mode of operation.